High vacuum



March 14, 1939. N EMBREE 2,150,676

HIGH VACUUM Filed Oct. 8, 1937 Norris Embree INVENI'OR BY ATTORNEYS Patented Mar. 14, 1939 UNITED STATES PATENT OFFICE HIGH VACUUM ware Application October 8, 1937, Serial No. 167,997 In Great Britain May 11, 1937 Claims.

This invention relates to improvements in high vacuum pumps and particularly condensation or diffusion pumps.

Due to the increasing use of high vacuum in 5 commercial and research activities, there has arisen a great demand for condensation pumps having high speeds. Since the production of the heretofore necessary very low backing pressures for condensation pumps operating with organic 1o vapors is decidedly expensive, there has also been a demand for condensation pumps which would operate against moderately high backing pressures.

This invention has for its object to provide a condensation pump having very high speeds of evacuation. A further object is to provide a multijet condensation pump which has a high speed and. which will operate against high backing pressures. Other objects will become apparent from the following detailed description.-

In the mushroom or umbrella condensation pump jet of conventional constructions, a vertical vapor tube, concentric with the main pump casing, is provided with a cap which serves to 5 deflect the vapors passing therethrough in a reverse direction into the annular space between the two. According to theory, the issuing vapors are supposed to pass directly downward as a more or less parallel stream and carry with them,

30 gases from the zone under exhaustion. I have found that vapors issuing from such a jet burst sideways or spread laterally and condense on the main casing at a position approximately opposite the edge of the jet. The vapors do not therefore pass in a direction which would result in good pumping speed. It has been found that if the central tube or chimney delivering vapors is externally constricted in the vicinity of the jet, the issuing vapors are not thrown sideways as heretofore, but pass in an approximately parallel stream resulting in very high pumping speeds. Also by constructing this jet so that it is of relatively small diameter, the admittance for the gases to be pumped is increased and the speed increases correspondingly.

In order to obtain both high pumping speeds and ability to work against high pressure, such a jet can be employed in conjunction with one or more jets which I have found are capable of working against high pressures. This provides a sufliciently low pressure to permit efficient operation of the high speed jet. The high pressure jet has a small clearance between its outer edge and the condenser wall. It is provided with an element which prevents expansion of the jet vapors until they. leave the jet edge and preferably another element which serves to streamline the flow of the vapors after they issue from the jet.

In the following description I have set forth 5 several examples of the preferred embodiments of my invention but it is to be understood that they are given by way of illustration and not in limitation thereof.

In the accompanying drawing I have illus- 1o trated preferred forms of pump and jet embodying the principles of my invention wherein like numbers refer to like parts and wherein:

Fig, 1 is a fragmentary vertical section of a condensation pump having the improved high 15 speed jet and: I

Fig. 2 is a vertical section of a condensation pump provided with the improved high speedhigh vacuum jet in combination with the im proved low pressure jet capable of operating 20 against relatively high backing pressures.

Referring to Fig. 1, numeral 2 designates the main casing of a condensation pump. Numeral 6 indicates the vapor delivery tube or chimney communicating at its lower end with the vapor 5 source (not shown) and at its upper end with the umbrella jet 8. The jet is formed by the mushroom cap made up of plate I0 and flange l2. It will be noted that chimney or vapor tube 6 is contracted immediately below the plate Ill 30 at Hi to form a concave cylinder or a surface which decreased in diameter in the vicinity of the jet. The plate Ill closes the upperend of chimney 6 and immediately below it are a series of openings, 16, whereby vapors in the chimney are permitted to flow into the jet. Numeral l5 designates a conical element supported by H, out of contact with hot cap l0 and serves to prevent gases from coming into contact with the plate and being heated and caused to flow in an opposite direction.

Referring to Fig. 2 main casing 2 is provided at its upper end with a ground edge 4 and at its base with a plate l8 forming a boiler for pump fluid 20. Chimney 6 is enlarged at its base at 22 so as to close ofi the boiler from the annular space between tubes 2 and 6. The walls at 22 are parallel to those of casing 2 and are sufliciently close to permit liquid to flow therethrough as a bead without permitting escape of vapors. 5 The chimney is centered by spider 2| and by the enlargement 22. Numeral 24 designates a truncated conical skirt, the small diameter of which snugly fits the walls of 6. A similar pair of skirts 26 and 28 the latter of which is reversed 55 are mounted upon 6 at a position below skirt 2% so as to form a passageway 30 therebetween. This passageway communicates with the interior of 6 by way of a plurality of openings 32. A second truncated cone 38 is mounted upon 6 at a position just below the restricted portion l4 and forms a jet 36 which is supplied with vapor by openings 38. The lower portion of main casing 2 is connected to a conduit elbow the vertical portion of which is provided with a beaded flange 42 and a series of fractionating rings 44. The upper ring is provided with a conduit 46 for re moval of light ends and the base of casing 2 is provided with a conduit 48 for introduction or removal of pump fluid.

During operation of the pump and jet illustrated in Fig. 1 pump vapors ascending through 6 pass through openings l6 and thence in a reverse direction through jet 8. Due to the constriction of 6 at [4, the issuing vapors are allowed to pass in a streamlined path towards the axis of the chimney and pump. For this reason the vapors take a general downward direction instead of issuing laterally or sideways as heretofore, which results in greatly increased pumping speed. All gases diffusing into this stream of vapor at the top of the pump are quickly passed with the vapor stream to the low pressure side of the pump instead of being forced backwards or held in a side bursting vapor stream as would happen with known constructions.

The construction shown results in greatly increased speed. It will be noted that the jet is of small diameter and by preference is of such diameter that there is a clearance of to 3" between the edge of the jet and the wall of the pump casing. This gives considerably greater speed, but smaller clearances can of course be used. This feature of construction is in direct contrast to the high vacuum jet clearances of the prior art wherein .5 to .6 cm. were usually recommended as a maximum clearance- The jet has an enormous pumping speed, but it is necessary, especially with the wide clearances to have a low backing pressure of below about .01 mm. This can be obtained by an efficient rotary oil pump, but I prefer to employ the jet in conjunction with a backing vapor jet which will operate against a high backing pressure and will produce a sufflciently low pressure for the high speed jet to efi'lciently operate. The apparatus of Fig. 2 is constructed to give such results.

During operation of the apparatus of Fig. 2 a pump fluid 20 such as di-amyl phthalate is introduced to the approximate level indicated and heat is applied to the base plate I 8. Flange 4 is connected to the system to be evacuated and 42 to a backing pump giving a pressure of about .1 to .3 mm. or less. Pump vapors pass upwardly through the chimney and some of them pass through openings 32 into the space between conical jet forming elements 24 and 26. These vapors then issue as a jet at 30 and pass downwards against the wall of easing 2 where they are condensed. Element 26 serves to preserve the jet as a high density stream and to direct it to the desired point or position of discharge and element 28 serves to streamline the jet after it has passed into the pumping zone. Due to these efi'ects and the small clearance this jet operates against a rather high backing pressure and reduces the pressure in the zone where jet 36 and especially jet 8 are located so that they can operate efliciently.

awasve The remaining vapors issue through jets 86 and 8. Jet 86 has a clearance intermediate that of jet 38 and 8 so that it operates against an intermediate pressure and produces a lower backing pressure for jet 8. It can be dispensed with, but adds to the balance and flne action of the jet combination. Jet 8 operates in the manner described in connection with Fig. 1. 1

Condensate flowsdown the walls of casing 2, which is cooled by air or water, between 22 and 2 and thence into the boiler. A bead of liquid persists between 22 and 2 so that escape of vapors in that direction is avoided. Light portions of the pump fluid and the pumped gases pass into conduit 40 and the pump fluid is condensed and, fractionated in rings 44. Useful constituents return to the boiler and light ends accumulate in the top ring and can be intermittently withdrawn through conduit 46.

As a specific example a pump almost identical to that illustrated in Fig. 2 was constructed to the, following dimensions.

Internal diameter of main casing 2; 3%" (96 cm.) Length of main casing 2--- 20" (51 cm.) Diameter of chimney 6 2%" O. D. (6.35 cm.)

Diameter of holes 32 19/64" (7.54 mm.) Diameter of holes 38 #19 drill (4.22 mm.) Diameter of holes l6 drill (2.06 mm.) Number of holes 32 20 Number of holes 38 38 Number of holes I6 32 Diameter of plate l0 36mm. Length of jet flange I2 10 mm. Angle of jet flange |2 8 Angle of jet flange 34"--- 12 Angle'of jet flange 24 12 Angle of elements 26 and 28 12 Clearance between 34 and wall of 2 12 mm, Clearance between 24 and Wall of 2 2mm.

Clearance between point of junction of 26 and 28 and wall of 2 4.5 mm. Clearance between point of junction of 26 and 28 and edge of 24 10 mm. Diameter of 14 at top 36 mm. Diameter of I4 1 cm. below top 26 mm. Diameter of l4 3.5 cm. be-

low top (min.) 21 mm.

This pump with di-amyl phthalate as a working fluid, afore pressure of .3 mm. and an input of 300 watts had a speed ranging from 220 liters to 250 liters a second measured at .0003 mm. on dry air (not hydrogen). times that which is obtained with known pumps of this size. The speed was the same with an input of 200 watts and a backing pressure of .17 mm.

It will'be noted that with this pump construction, the expansion ratio progressively increases from the low to the high pressure side of the pump. Thus, in .the high pressure jet 30 little or no expansion is permitted. At 'jet 36 increased expansion takes place and at jet l2 still greater expansion is permitted.

The clearance between the edge of the high vacuum jet and the wall of the pump can be between about and 3", the smaller being used with smaller pumps or pumps which must op- This speed is many erate against higher backing pressures with sacrifice in speed. The larger clearances are best used in larger pumps and with good sources of backing pressure and give higher speeds. By high backing pressures is of course included a backing pressure produced by an auxiliary jet as in Fig. 2. The clearance of the high pressure jet 3!! of Fig. 2 should be between about 1 and 4 mm. depending upon the pressure against which it is to operate and the speed desired. With clearances of much less than 2 mm., a bead of liquid sometimes forms. The high vacuum jet flange l2 can vary considerably from perpendicular.

The best angle will depend upon the slope of constriction M. For best operation a flange angle inwardly of 10 or outwardly of 30 or any angle therebetween should be used. To illustrate, with a chimney slope at 5 of 30 and a jet flange I 2 slope inwards of the pumping speed was 240 liters per second. With a vertical jet flange the speed was 245 liters and with a jet flange sloping outwardly the speed was the same. The optimum is therefore between vertical and 15 outward slope. The constriction in the chimney particularly in that portion which forms the inside jet wall is of course the most essential feature.

It is apparent that many changes can be made in the above described apparatus without departing from the spirit or scope of my invention. Any suitable construction material can be employed and it is preferred that the surfaces in contact with gases or vapors be smooth to offer slight resistance to their flow. Bakelite, glass and metals are examples of suitable materials. An efiicient combination is a main casing made of glass, to permit observance of the pump action, and jets etc. made of spun aluminum. Element l5 which prevents heating and consequent rebounding of gases from hot plate I0 is advantageous but can be eliminated without much effect upon the operation of the pumps. The streamlining element 28 can likewise be eliminated, but it materially contributes to the pumping action. The constriction at M need not be circular. For instance, it can be parabolic, hyperbolic or straight line constrictions such as two truncated cones with their widest bases at H) and 36 and the narrow truncated portions joining at I 4. In other words, the essential characteristic is the constriction to enable expansion of the vapors towards the center axis of the pump immediately below the umbrella jet, resulting in the vapors passing downwards or parallel to the condenser wall instead of laterally. A curved shape such as illustrated is preferred since it streamlines the flow of the vapor stream. The number of jets in Fig. 2 can be varied greatly, thus jet 36 can be eliminated or 2 or more jets used in its place. The condensing area of the main casing is shown as being air cooled, but can be provided with fins or jacketed for circulation of cooling fluid if desired. Pump fluids such as mercury and organic liquids of low vapor pressure are well known and can be employed as a class in the pumps described.

Because oi! its novel construction the high vacuum jet permits evacuation at unusually high speeds and the low vacuum jet permits efiicient operation against unusually high backing pressures. By employing the two jets in series a pump results which has all of the advantages of both, namely ability to operate against high backing pressures with phenomenal speeds. The improved high pressure jet has other advantages. Due to element 26, which prevents expansion of jet vapors until they reach the edge or lip of 24, the vapors are conserved as a dense stream and therefore less vapors are necessary to accomplish the same amount of work. This means a considerable saving in power expenditure in the form of heat.

What I claim is:

l. A condensation pump provided with an umbrella jet within a pump casing serving as a condenser wall which jet is supplied with actuating vapor by a chimney communicating with a boiler, characterized by the fact that the inner umbrella. jet wall and the chimney wall in the vicinity of the jet slant inwardly with respect to the casing wall so as to permit vapors issuing from the jet to pass or expand in a direction .approximately parallel to the condenser walls.

2. A condensation pump provided with a plu-' rality of umbrella jets operating in series and supplied with working vapors by a common chimney characterized by the fact that the jet operating against the highest pressure is provided with an element which substantially prevents expension of the jet vapors until they leave the outside tip of the jet and by the fact that the outside surface of the chimney delivering vapor to the jet operating against the lowest pressure and the inside wall of the jet gradually decrease in diameter in the vicinity of the jet and in the direction in which the vapors pass from the jet.

3. A condensation pump provided with a pump casing within which are located a plurality of umbrella jets adapted to operate in series characterized by the fact that the jet which operates against the highest pressure is provided with an element which substantially prevents expansion of the jet vapors until they leave the lip of the jet and by the fact that the jet which operates against the lowest pressure is an expansion type umbrella jet, the inside wall of which slants inwardly with respect to the casing, from the throat to the mouth of the jet so as to permit vapors issuing from the jet to pass or expand towards the center of the pump.

4. A condensation pump provided with a main pump casing within which is disposed a jet having an inside and outside wall characterized by the fact that the inside wall of the jet slants inwardly with respect to the side wall of the condensation pump casing, substantially the entire distance from the throat to the mouth of the jet, whereby the vapors as they issue from the jet are permitted to expand toward the center of the pump.

5. A condensation pumpprovided with an umbrella jet located inside the pump casing, which jet is supplied with actuating vapor by a chimney communicating with a boiler, characterized by the fact that the inner jet wall slants inwardly with respect to the casing wall substantially the entire distance from the throat to the mouth of the jet and the outside wall of the jet slants outwardly with respect to the casing wall so as to form an angle of between 15 and 30 with the pump casing axis.

NORRIS D. EMBREE. 

